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Phc News - Features: May 2010: Efficient air-to-water heat pumps arriving in America

Efficient air-to-water heat pumps arriving in America


For the first time ever hydronic contractors are positioned to catapult to the forefront of green building with the arrival in North America of new factory packaged, integrated heating and cooling devices that have high efficiencies and great solar-thermal tie-ins. This exciting new generation of air-to-water heat pumps, based on variable speed inverter technology, offers hydronics a huge new opportunity.

Until now, radiant floor heating and other forms of hydronic heating have required the additional expense and technical complexity of incorporating a second distinct hvac system to do cooling. With these new appliances, dual heating and cooling will require only a handful of adjustments to hydronic practice: adding air handlers with condensate drains, changeover valves and some insulated piping.

While air-to-air heat pumps have been well established in North America, these highly efficient and packaged air-to-water heat pumps are just what the hydronic industry needs to make a next growth surge. Previous air-to-water reverse cycle chillers and heat pumps did not feature variable speeds, nor were they packaged as well integrated units for heating, cooling and domestic hot water with solar thermal options. The older models were less efficient and often noisy. That’s changing now with the introduction into North America of this sophisticated new generation of air-to-water heat pumps based on variable speed inverter technology.

The recently introduced Daikin Altherma, as well as introductions by Mitsubishi, Toshiba, Aermec and others, will offer hvac and hydronic contractors great new possibilities for heating/cooling and tie-ins with solar thermal. This spells tremendous opportunity in both commercial and residential applications for hydronic contractors — if they take advantage of it.

How it works: Hot

Sophisticated controls, with inverter technology to run a variable speed compressor, reduces cycle losses, and the big turn down ratio adds comfort by load matching, saves electricity and extends the life of the compressor. Heated water is made by means of a refrigerant-to-water heat exchanger. Most of these units come packaged to do both heating and cooling, with a strategy to make — or at least to preheat —domestic water, and tie-ins to solar thermal systems.

How it works: Cold

Run in reverse, cooling may be taken off the refrigerant side with a direct expansion (dx) coil, or chilled water may be generated with the refrigerant-to-water heat exchanger. Different manufacturers are making different choices in their initial offering in terms of which way to do cooling. For the residential market most companies are offering cooling with chilled water. For hydronic contractors, cooling with chilled water opens up a huge new aspect of our trade — one that uses familiar piping and pumping methods.

High performance and green appeal

These units can offer high coefficients of performance (cop) that, particularly in milder climates, are competitive with geothermal heat pumps, while at the same time offer much simpler, less environmentally intrusive and less costly installations. Manufacturers claim heating cops in the range of 3.0 to as high as 5 in milder climates. At these efficiencies, these units offer a significantly lower carbon footprint than fossil fuel choices, even after allowing for all the distribution losses and fossil fuel contribution for the North American electric grid, making it an obvious choice for green building. Since the units reduce the overall energy consumption of a project, it becomes even more cost feasible to offset the overall energy use of a project with PV.

David Knight of the Monterey Energy Group in Monterey, California has now specified close to 100 Daikin Altherma’s — all with solar inter-tie, and most also with pv — to get to net zero. He notes the declining cost of pv will make this even more attractive.

“Combining these multi-purpose heat pumps with pv is particularly appealing to energy conscious clients and a good fit in states like Oregon, California and others that have good pv rebates,” Knight said. “It insulates them from future increases in energy costs. And economically, it is particularly attractive in areas with low electric rates or areas without natural gas.”

Design advantage: Hydronics

To take advantage of this new opportunity, hydronic contractors will need to master and correctly apply the design constraints of the units. Good hydronic contractors are skilled at the calculations required for effective design. On the heating side, these heat pumps produce modest water temperatures (120°F-130°F). With radiant floor heating this will require the use of high output radiant floor assemblies, will place limitations on the R-Value of floor coverings, and requires careful design. And while forced air fan coils may be used, they must be units with extra rows of coils specifically designed for lower water temperatures.

Cooling with chilled water will mean that hydronic contractors will have to learn about selecting fan convectors with condensate drains, and must also insulate pipes against condensation. As outdoor temperature decreases, the output of the unit also decreases, so each unit must be sized at the design temperature. However, since the variable speed inverter technology has such high turn down ratios (such as 5:1) this is not much of a problem. Another design issue is that the units may efficiently make domestic hot water, but will only recover according to the sizing of the unit.

As this technology arrives here from abroad, we need to understand some distinctions. Today’s small, tighter, more efficient homes often mean these units can be small in output for heating and cooling. Even so, most Americans demand more hot water than their European or Asian counterparts. Many American contractors are realizing this means installing bigger domestic water tanks than has been normal in Europe or Asia.

To optimize the efficiencies and for lowest operating costs, contractors and operators will have to become knowledgeable about how to schedule and control these sophisticated units so that the use of back up heat is kept to a minimum. Selecting the best air-to-water heat pumps with regard to domestic hot water production may require some careful probing, since the units will likely be rated in heating and cooling, rather than for their domestic hot water capability. However, units that are not integrated in the production of heating and domestic hot water are likely to be compromising domestic hot water production, efficiency or both.

These newer air-to-water heat pumps are crossover products, with several constituencies vying for control. There is considerable debate over who should distribute, support, sell and install these products. The heat pump end is more traditionally an hvac product with refrigerant, and the other end is a hydronic product that requires knowledge of hydronic design and installation. This is a perfect opportunity for specialty hydronic contractors, as they have a much bigger incentive to develop the market for these products than air side competitors, since, unlike many hvac contractors, hydronic contractors are not already selling air-to-air heat pumps.

The next few years will determine whether smart, strategic hydronic contractors succeed in taking the lead in this business, or whether it languishes with the more traditional air side businesses as just an option to air-to-air. This is a perfect time for hydronic contractors to learn about cooling with chilled water and about the refrigeration technology in the heat pumps.

Because these air-to-water heat pumps are so new to the North American market, they have yet to garner the political support to qualify them for federal tax credits. Similarly, North American testing standards have not yet been established. The best test data on these units is from Europe and Asia; there is no current standard in the US for testing inverter technology air-to-water heat pumps.

The only choice now is to test them according to air-to-air procedures, but these do not reflect the efficiencies of air-to-water and variable speed inverter technology — these tests call only for a low and a high speed test, and do not account for the fact that with variable speed technology a unit will almost always be running somewhere in between.

Again, this is a great opportunity for hydronic industry leadership. While these political and test data issues may slow North American adoption of this air-to-water technology, the benefits of these new units are so obvious that they are already gaining market acceptance. Already, electric utilities are testing them for inclusion in rebate programs. The combination of efficiency, a low carbon footprint, and the triple-threat ability to provide heating, cooling and domestic hot water, all with a solar thermal option, means these new air- to-water heat pumps should generate a big growth in hydronics. It’s largely up the hydronic industry to embrace it.

Hoyt Corbett is a patented inventor and develops products for Precision Hydronic Products. His products may be found at and Reach him at inventive


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